A Meta-Analysis of Global Urban Land Expansion

Karen C Seto,Michael K Reilly,Michail Fragkias,Burak Güneralp

doi:10.1371/journal.pone.0023777

Abstract

The conversion of Earth's land surface to urban uses is one of the most irreversible human impacts on the global biosphere. It drives the loss of farmland, affects local climate, fragments habitats, and threatens biodiversity. Here we present a meta-analysis of 326 studies that have used remotely sensed images to map urban land conversion. We report a worldwide observed increase in urban land area of 58,000 km2 from 1970 to 2000. India, China, and Africa have experienced the highest rates of urban land expansion, and the largest change in total urban extent has occurred in North America. Across all regions and for all three decades, urban land expansion rates are higher than or equal to urban population growth rates, suggesting that urban growth is becoming more expansive than compact. Annual growth in GDP per capita drives approximately half of the observed urban land expansion in China but only moderately affects urban expansion in India and Africa, where urban land expansion is driven more by urban population growth. In high income countries, rates of urban land expansion are slower and increasingly related to GDP growth. However, in North America, population growth contributes more to urban expansion than it does in Europe. Much of the observed variation in urban expansion was not captured by either population, GDP, or other variables in the model. This suggests that contemporary urban expansion is related to a variety of factors difficult to observe comprehensively at the global level, including international capital flows, the informal economy, land use policy, and generalized transport costs. Using the results from the global model, we develop forecasts for new urban land cover using SRES Scenarios. Our results show that by 2030, global urban land cover will increase between 430,000 km2 and 12,568,000 km2, with an estimate of 1,527,000 km2 more likely.

Highlights

Earth’s land surface is a finite resource that is central to human welfare and the functioning of the Earth system
We developed four urban land expansion scenarios based on the Special Report on Emissions and Scenarios (SRES) Scenarios available through Center for International Earth Science Information Network (CIESIN)
Our results show considerable variation in the rates of urban expansion over the study period, with the highest rates in China followed closely by Southwest Asia (Figure 2)

Summary

Introduction

Earth’s land surface is a finite resource that is central to human welfare and the functioning of the Earth system. On the continuum of anthropogenic activities, urbanization is the most irreversible and humandominated form of land use. Urbanization results in changes in land-cover, hydrological systems, biogeochemistry, climate, and biodiversity [2]. In the United States, urban expansion in the form of housing development is a major threat to protected areas [5]. Urban areas affect their local climate through the modification of surface albedo and evapotranspiration, and increased aerosols and anthropogenic heat sources, resulting in elevated temperatures [6] and changes in precipitation patterns [7,8]. The spatial form of cities, especially urban transportation infrastructure and residential density, affects travel demand [9], energy consumption [10], and automobile use [11]

Methods

Results

Conclusion